Transmission of Nerve Impulses — Easy NEET Notes
18.3.2 Transmission of Impulses
1. What is a nerve impulse?
- A nerve impulse is an electrical signal that travels through a neuron.
- It helps in communication between different parts of the body.
2. What is a Synapse?
- A synapse is the junction between two neurons.
- Through this junction, nerve impulses pass from one neuron to another.
Structure of Synapse
A synapse is formed by:
- Pre-synaptic neuron → neuron sending the impulse
- Post-synaptic neuron → neuron receiving the impulse
- Synaptic cleft → small gap between the two neurons
Types of Synapses
A. Electrical Synapse
Features
- Pre- and post-synaptic membranes are very close.
- Electrical current flows directly from one neuron to another.
- Impulse transmission is very fast.
Important Points
- Similar to impulse conduction along one axon.
- Faster than chemical synapse.
- Rare in humans.
NEET Point
- No neurotransmitter is required.
B. Chemical Synapse
Features
- Neurons are separated by a fluid-filled gap called synaptic cleft.
- Impulse transmission occurs using chemicals called neurotransmitters.
Important Points
- Most common type in humans.
- Transmission is slower than electrical synapse.
Neurotransmitters
Definition
- Chemical substances that carry impulses across the synaptic cleft.
Examples
- Acetylcholine
- Dopamine
- Serotonin
- Noradrenaline
Synaptic Vesicles
Meaning
- Small sacs present in axon terminals.
- Filled with neurotransmitters.
Function
- Store and release neurotransmitters during impulse transmission.
Steps of Transmission Across Chemical Synapse
Step 1: Arrival of Impulse
- Action potential reaches the axon terminal.
Step 2: Vesicle Movement
- Synaptic vesicles move toward the pre-synaptic membrane.
Step 3: Fusion
- Vesicles fuse with the plasma membrane.
Step 4: Release of Neurotransmitters
- Neurotransmitters are released into the synaptic cleft.
Step 5: Binding to Receptors
- Neurotransmitters bind to receptors on post-synaptic membrane.
Step 6: New Impulse Generation
- A new electrical impulse is generated in the next neuron.
Diagram Labels and Functions
Axon
- Conducts nerve impulses away from cell body.
Axon Terminal
- End part of axon where neurotransmitters are released.
Synaptic Vesicles
- Store neurotransmitters.
Pre-synaptic Membrane
- Membrane of neuron sending impulse.
Synaptic Cleft
- Gap between two neurons.
Post-synaptic Membrane
- Membrane of receiving neuron.
Receptors
- Receive neurotransmitters and start new impulse.
Difference Between Electrical and Chemical Synapse
| Feature | Electrical Synapse | Chemical Synapse |
|---|---|---|
| Gap between neurons | Very small | Synaptic cleft present |
| Transmission | Direct electrical flow | Neurotransmitters |
| Speed | Very fast | Slower |
| Neurotransmitter needed | No | Yes |
| Occurrence | Rare | Common |
Important NEET Keywords
Synapse
Junction between two neurons.
Synaptic Cleft
Gap between neurons.
Neurotransmitter
Chemical messenger transmitting impulses.
Action Potential
Temporary electrical change during impulse transmission.
Receptor
Protein receiving neurotransmitter signal.
NCERT Important Lines for NEET
- Synapse is the functional junction between two neurons.
- Two types of synapses are electrical and chemical synapses.
- Electrical synapses are faster than chemical synapses.
- Neurotransmitters help in transmission across chemical synapse.
- Synaptic vesicles contain neurotransmitters.
Memory Trick
“VFRB”
For chemical synapse steps:
- V → Vesicles move
- F → Fuse with membrane
- R → Release neurotransmitter
- B → Bind to receptors
One-Line Revision
- Synapse = junction between neurons.
- Electrical synapse = fast direct transmission.
- Chemical synapse = neurotransmitter-mediated transmission.
- Synaptic vesicles store neurotransmitters.
- Receptors receive chemical signals.
 |
| Diagram showing transmission of nerve impulses across a chemical synapse in neurons. |
CBSE Class 11 Biology Questions
Chapter: Transmission of Impulses (Synapse)
1. MCQs (Multiple Choice Questions)
1. The junction between two neurons is called:
A. Axon
B. Dendrite
C. Synapse
D. Node of Ranvier
Answer: C. Synapse
2. The gap between two neurons is known as:
A. Axoplasm
B. Synaptic cleft
C. Myelin sheath
D. Schwann cell
Answer: B. Synaptic cleft
3. Neurotransmitters are stored in:
A. Nucleus
B. Mitochondria
C. Synaptic vesicles
D. Ribosomes
Answer: C. Synaptic vesicles
4. Which type of synapse is faster?
A. Chemical synapse
B. Electrical synapse
C. Both equal
D. None
Answer: B. Electrical synapse
5. In chemical synapse, transmission occurs through:
A. Hormones
B. Enzymes
C. Neurotransmitters
D. Oxygen
Answer: C. Neurotransmitters
6. The membrane of the receiving neuron is called:
A. Pre-synaptic membrane
B. Post-synaptic membrane
C. Plasma membrane
D. Axonal membrane
Answer: B. Post-synaptic membrane
7. Electrical synapses are:
A. Common in humans
B. Slower than chemical synapses
C. Rare in humans
D. Found only in muscles
Answer: C. Rare in humans
8. Which structure receives neurotransmitters?
A. Axon
B. Vesicles
C. Receptors
D. Myelin sheath
Answer: C. Receptors
9. The impulse reaching axon terminal is called:
A. Reflex
B. Hormone
C. Action potential
D. Stimulus
Answer: C. Action potential
10. Synaptic vesicles fuse with:
A. Nucleus
B. Plasma membrane
C. Cytoplasm
D. Ribosome
Answer: B. Plasma membrane
2. Very Short Answer Questions (1 Mark)
Q1. Define synapse.
Answer: Synapse is the junction between two neurons where transmission of nerve impulse occurs.
Q2. What is synaptic cleft?
Answer: Synaptic cleft is the gap between pre- and post-synaptic neurons.
Q3. Name the chemical messengers involved in impulse transmission.
Answer: Neurotransmitters.
Q4. Which synapse is faster?
Answer: Electrical synapse.
Q5. Where are neurotransmitters stored?
Answer: In synaptic vesicles.
3. Short Answer Questions (2–3 Marks)
Q1. Differentiate between electrical and chemical synapse.
| Electrical Synapse | Chemical Synapse |
|---|---|
| Faster transmission | Slower transmission |
| No neurotransmitter needed | Neurotransmitter needed |
| Membranes very close | Synaptic cleft present |
Q2. Write the role of neurotransmitters.
Answer:
- Neurotransmitters transmit impulses across synaptic cleft.
- They are released from synaptic vesicles.
- They bind to receptors on post-synaptic membrane.
Q3. What happens when an action potential reaches axon terminal?
Answer:
- Synaptic vesicles move toward membrane.
- Vesicles fuse with plasma membrane.
- Neurotransmitters are released into synaptic cleft.
4. Long Answer Questions (5 Marks)
Q1. Explain the mechanism of transmission of impulse across chemical synapse.
Answer:
- Action potential reaches axon terminal.
- Synaptic vesicles move toward pre-synaptic membrane.
- Vesicles fuse with plasma membrane.
- Neurotransmitters are released into synaptic cleft.
- Neurotransmitters bind to receptors on post-synaptic membrane.
- A new impulse is generated in post-synaptic neuron.
Q2. Describe structure and types of synapse.
Answer:
Structure of Synapse
- Pre-synaptic neuron
- Synaptic cleft
- Post-synaptic neuron
Types of Synapse
Electrical Synapse
- Very small gap
- Direct current flow
- Fast transmission
Chemical Synapse
- Synaptic cleft present
- Neurotransmitter involved
- Slower transmission
5. Assertion and Reason Questions
Q1.
Assertion (A): Electrical synapses are faster than chemical synapses.
Reason (R): Electrical current flows directly between neurons.
A. Both A and R are true and R is correct explanation
B. Both A and R are true but R is not correct explanation
C. A is true but R is false
D. A is false but R is true
Answer: A
Q2.
Assertion (A): Neurotransmitters are released in electrical synapse.
Reason (R): Chemical synapse requires neurotransmitters.
Answer: D
(A is false but R is true)
Q3.
Assertion (A): Synaptic vesicles contain neurotransmitters.
Reason (R): Vesicles help in transmission of impulses.
Answer: A
6. Fill in the Blanks
- Junction between two neurons is called synapse.
- Gap between neurons is called synaptic cleft.
- Neurotransmitters are stored in synaptic vesicles.
- Electrical synapse is faster than chemical synapse.
- Receptors are present on post-synaptic membrane.
- The electrical signal in neuron is called nerve impulse.
7. Match the Column
| Column A | Column B |
|---|---|
| 1. Synaptic cleft | (c) Gap between neurons |
| 2. Neurotransmitter | (d) Chemical messenger |
| 3. Synaptic vesicle | (a) Stores neurotransmitter |
| 4. Receptor | (b) Receives chemical signal |
Answers
1 → c
2 → d
3 → a
4 → b
8. Statement-Based Questions
Q1. Identify True/False
- Chemical synapse uses neurotransmitters. → True
- Electrical synapse is slower. → False
- Synaptic cleft is absent in electrical synapse. → True
- Receptors are present on pre-synaptic membrane. → False
9. Case Study Questions
Case Study
A student observed that when an impulse reaches the axon terminal, certain chemicals are released into a gap and bind to receptors of another neuron.
Q1. Name the chemicals released.
Answer: Neurotransmitters
Q2. Name the gap between neurons.
Answer: Synaptic cleft
Q3. Which type of synapse is described here?
Answer: Chemical synapse
Q4. Where are neurotransmitters stored?
Answer: Synaptic vesicles
10. Important Diagram-Based Questions
Q1. Label the following parts:
- Axon terminal
- Synaptic vesicles
- Synaptic cleft
- Receptors
- Post-synaptic membrane
Q2. Which structure stores neurotransmitters?
Answer: Synaptic vesicles
11. HOTS Questions
Q1. Why are electrical synapses faster than chemical synapses?
Answer:
Because electrical current passes directly from one neuron to another without the use of neurotransmitters.
Q2. Why is transmission across chemical synapse one-way?
Answer:
Because neurotransmitters are released only from pre-synaptic neuron and receptors are present only on post-synaptic membrane.
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